Balanced codewords for reducing a selected state in memory cells

Abstract

Methods, systems, and devices for balanced codewords for reducing a selected state in memory cells are described. A memory device may divide a sequence of data bits into sets of bits associated with different bit-positions in a coding scheme. The memory device may then balance a first codeword that includes the first set of the data bits in the binary domain to reach a target ratio of logic values for the codeword. Using the first codeword and the other set(s) of data bits, the memory device may balance the remaining two states in the state domain to reach an overall target distribution of the three states. The memory device may then generate one or more codeword(s) for the other set(s) of data bits so that the memory device can write all of the codewords to ternary cells.

What is claimed is: 
     
       1. A method, comprising:
 dividing a sequence of bits into a first set of bits and a second set of bits; 
 inverting a first portion of a first codeword that comprises the first set of bits to reach a first target ratio of logic values in the first codeword; 
 determining, after inverting the first portion and based at least in part on a coding scheme, a set of states associated with the second set of bits and the first set of bits including the inverted first portion; 
 changing a subset of the set of states to reach a second target ratio of states in the set of states; 
 determining, based at least in part on the coding scheme, a second portion of the second set of bits associated with the changed subset of the set of states; and 
 writing, to a set of memory cells according to the coding scheme, the first codeword and a second codeword comprising the second set of bits including the second portion. 
 
     
     
       2. The method of  claim 1 , wherein the set of memory cells comprises ternary memory cells programmable to a first state, a second state, and a third state, and wherein the coding scheme maps three bits to a pair of ternary cells. 
     
     
       3. The method of  claim 2 , further comprising:
 determining a third target ratio for the first state, the second state, and the third state; and 
 selecting the coding scheme used to determine the set of states based at least in part on the third target ratio. 
 
     
     
       4. The method of  claim 2 , further comprising:
 determining a polarity of a read voltage used for sensing the set of memory cells; and 
 selecting the coding scheme used to determine the set of states based at least in part on the polarity. 
 
     
     
       5. The method of  claim 2 , wherein the first set of bits in the first codeword comprises bits assigned to a first bit-position associated with the three bits, and wherein the second set of bits in the second codeword comprises bits assigned to a second bit-position associated with the three bits. 
     
     
       6. The method of  claim 5 , wherein the second set of bits in the second codeword comprises bits assigned to a third bit-position associated with the three bits. 
     
     
       7. The method of  claim 5 , wherein dividing the sequence of bits comprises:
 dividing the sequence of bits into a third set of bits that comprises bits assigned to a third bit-position associated with the three bits, wherein the set of states is associated with the third set of bits; and wherein inverting comprises:
 determining, based at least in part on the coding scheme, a third portion of the third set of bits associated with the changed subset of the set of states, wherein a third codeword comprising the third set of bits including the third portion is written to the set of memory cells. 
 
 
     
     
       8. The method of  claim 1 , further comprising:
 generating, before inverting the first portion of the first codeword, parity bits that are based at least in part on the first set of bits, wherein the first codeword comprises the parity bits. 
 
     
     
       9. The method of  claim 1 , further comprising:
 generating, after inverting the second portion of the second set of bits, parity bits based at least in part on the second set of bits, wherein the second codeword comprises the parity bits. 
 
     
     
       10. The method of  claim 1 , further comprising:
 storing a first set of balancing information bits that indicates the inverted first portion of the first codeword; and 
 storing a second set of balancing information bits that indicates the second portion of the second set of bits. 
 
     
     
       11. The method of  claim 10 , further comprising:
 adding, after inverting the first portion of the first codeword and based at least in part on the first set of balancing information bits, at least one padding bit to the first set of bits, wherein the set of states is based at least in part on the at least one padding bit. 
 
     
     
       12. An apparatus, comprising:
 an array of memory cells comprising a set of memory cells; and 
 a controller coupled with the array of memory cells and configured to cause the apparatus to:
 divide a sequence of bits into a first set of bits and a second set of bits; 
 invert a first portion of a first codeword that comprises the first set of bits to reach a first target ratio of logic values in the first codeword; 
 determine, after inverting the first portion and based at least in part on a coding scheme, a set of states associated with the second set of bits and the first set of bits including the inverted first portion; 
 change a subset of the set of states to reach a second target ratio of states in the set of states; 
 determine, based at least in part on the coding scheme, a second portion of the second set of bits associated with the changed subset of the set of states; and 
 write, to the set of memory cells according to the coding scheme, the first codeword and a second codeword comprising the second set of bits including the second portion. 
 
 
     
     
       13. The apparatus of  claim 12 , wherein the controller is further configured to cause the apparatus to:
 determine a third target ratio for a first state, a second state, and a third state; and 
 select the coding scheme used to determine the set of states based at least in part on the third target ratio.